The present invention generally relates to a device for providing relative angular adjustment between at least two drivingly connected shafts and more particularly to such a device having a compact design and reliable operation.
German Published Unexamined Patent Application (DE-OS) No. 3,126,620 discloses a device for altering the phase setting between an engine shaft and a control shaft in the case of engines which have two separate control shafts for intake valves and outlet valves, the device permitting alternation between two different timing settings. Each of the two timing settings corresponds to one end position of a movable driving member which is connected to an engine shaft and a control shaft via couplings, of which at least one is provided with a helical toothing, and by axial displacement brings about a rotation of the control shaft relative to the engine shaft.
The adjustment of the driving member into one of the end positions is effected by the prestress of a spring, while the adjustment into the other end position is effected via pressure oil from the engine oil circuit. A centrifugally actuated slide assumes three different positions depending on the engine speed, in which positions it correspondingly opens and closes oil discharge bores and hence controls the oil pressure on the driving member. In a slide position opening an oil discharge bore, below a certain engine speed, the driving member is acted upon by a spring force only, which holds the driving member in one end position.
If the engine speed exceeds this first threshold value, the slide closes the oil discharge bore as a result of the change in the centrifugal force and the driving member is displaced axially counter to the spring stress by the increasing engine oil pressure into a second end position. As a result, a relative rotation takes place between the engine shaft and the control shaft and a timing setting matched to this engine operating condition is thereby achieved. After a further threshold value for the engine speed has been exceeded, the slide is moved into a position which makes an oil discharge possible again. By virtue of the spring force, the driving member is moved back into its first end position again, with corresponding relative rotation. The adjustment of the driving member when the engine speed falls below the threshold values takes place in the same manner.
German Published Unexamined Patent Application (DE-OS) No. 3,316,162 shows a comparable device, except that the actuation of the driving member is not controlled by centrifugal forces, the slide controlling the oil flow being electromagnetically actuatable instead.
Both devices mentioned above have the disadvantage that control takes place via an influencing of the oil discharge. In one of the two working positions of the driving member, a continuous oil flow with the associated losses is present.
A further disadvantage consists in the fact that, in the case of a resetting procedure into the starting position, the oil forced out of the working space by the driving member as a result of the spring force has to be discharged via the same oil discharge bore through which the oil, in this position of the slide, flows continuously is channelled. This state of affairs results in an undesirable slowing of the resetting procedure.
At low engine speeds, e.g. during idling, the oil pressure is too low to bring about an adjustment. For this reason, the driving member must be brought into the position corresponding to this operating condition by spring force. However, at low speed and hence also low oil pressure, such a spring force can hinder an adjustment of the driving member by pressure oil in those time periods in which a restraining camshaft torque is present, with the result that an adjustment can only take place when a driving camshaft torque is operative, i.e. intermittently. In order to avoid the undesired resetting of the driving member caused by the spring force together with the camshaft torque, the helical toothing must be of irreversible design, i.e. must be designed to have a shallow helix angle. However, such a helix angle also permits only a short adjustment path, i.e. the relative angular adjustment between engine shaft and control or camshaft is small, as is also, therefore, the influence of a timing alteration.
A similar adjusting device is also described in U.S. Pat. No. 4,305,367. Admittedly, this does not relate to a relative angular adjustment between an engine shaft or crankshaft and a control shaft or camshaft for setting the valve timing, as described in the two cited publications, but to an adjustment of a control shaft for an injection pump. In contrast to the above-indicated devices, the driving member, which is likewise provided with helical toothing and is designed as an annular piston, is subjected alternately to pressure oil from one side or the other, depending on the desired direction of movement. The pressure oil is supplied by means of a specially allocated oil pump via control devices and separate lines to the two working spaces, which are separated by the annular piston. Compared to an internal oil supply and control, this represents a considerably greater expenditure in terms of construction.
It is an object of the invention, while avoiding the disadvantages mentioned, to provide a device of the generic type in such a way that, in combination with compact design, an angular adjustment takes place reliably and quickly over a wide range, irrespective of the oil pressure.
It is another object of the present invention to provide a device for permitting angular adjustment between connected shafts which is relatively simple to construct in an inexpensive manner and provides a large range of angular adjustment relative to a simultaneously short axial adjustment path.
These and other objects are achieved according to the teachings of the present invention by eliminating the need for a spring member to return the driving member to its original position due to a unique arrangement driven essentially by hydraulic pressure to provide a greater positioning movement without the need for continuous oil flow. Further embodiments and advantages of the invention will become evident from the appended claims and following the description.
According to certain advantageous features of preferred embodiments of the present invention, a sprocket wheel, which is driven by a crankshaft via a chain connection, is mounted on a sprocket wheel carrier designed as a hollow shaft and having an inner helical toothing. A positioning piston provided with a corresponding outer helical toothing is guided in the sprocket wheel carrier so as to be axially movable. Via its likewise helical inner toothing, this piston is connected in an axially displaceable manner to an outer helical toothing of a hollow flanged shaft rigidly connected to the camshaft.
Sprocket wheel carrier, camshaft and flanged shaft together form an annular hollow space which is divided by the positioning piston into two working spaces. Arranged in the hollow flanged shaft is a control piston which has two working positions, is held in one of the these working positions by a spring and can be moved by an armature, rigidly connected to it, of an electromagnet fixed in relation to the engine into the other working position, counter to the force of the spring. Depending on the position of the control piston the feeding of pressure oil from the engine oil circuit via the oil bore of the camshaft is possible via an annular space formed by the control piston and via oil feed bores to one of the two working spaces.
The control piston simultaneously blocks the discharge from the second working space, which is shut off from the oil feed, for the purpose of emptying the latter via a longitudinal bore in the interior of the control piston and a bore in the camshaft. The positioning piston is adjusted by hydraulic pressure only in both directions and does not require a separate spring force for resetting.
Thus no spring force has to be overcome during the adjustment of the positioning piston and a greater positioning moment can be achieved as a result. Since the particular working space under pressure is shut off from the oil discharge, a continuous oil flow does not take place either. Oil flow only takes place in the time periods corresponding to the emptying of the particular working space, i.e. during an adjustment procedure until one of the two working positions is reached.
In the base position, the electromagnet is preferably de-energized and the control piston is held in one end position by the spring. After the magnet is switched on, the control piston is moved into the other end position counter to the spring force. By virtue of the resulting feeding of pressure oil into one of the two working spaces, the positioning piston is displaced axially and, via the helical toothing, rotates the flanged shaft, and hence also the camshaft, relative to the sprocket wheel driven by the crankshaft.
Oil is pushed out of the other working space in the particular case by the axial displacement of the positioning piston and is discharged to the engine oil circuit. When the electromagnet is switched off, the control piston returns to its starting position with the aid of the spring force, permits oil discharge from the working space which has up to this time been under pressure and feeds pressure oil to the other working space. By means of this renewed positioning procedure, the previous rotation is reversed again.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.